Bacteria of subclass γ-Proteobacteria associated with commercial Argopecten purpuratus (Lamark, 1819) hatcheries in Chile

The management of bacterial loading in intensive aquaculture systems is often a key factor in the success of larval cultures, particularly in molluscan hatcheries. Vibrio spp. have often been cited as affecting scallop larvae cultures. Bacteriological studies employing emergent molecular methods may now be of use in molluscan hatcheries to monitor the abundance of total and non-culturable Vibrio spp. In this study, the fluorescence in situ hybridization (FISH) technique with 16S rRNA-targeted oligonucleotide probes was used to quantify the presence of γ-Proteobacteria and Vibrio spp. in the bacterioplankton associated to mass larval cultures in six commercial hatcheries in two geographic regions of northern Chile. Results showed an average of 58% (Region III) and 38% (Region IV) of total cell counts could be detected by hybridization by using probe for domain Eubacteria. Use of the probe for γ-Proteobacteria showed averages between 21% and 28% in these regions, and use of the probe for Vibrio spp. detected percentage between 0.6% and 17%. Direct counts by fluorescence compared with viable plate counts suggested low culturability of the bacterioplankton. Results obtained from the different sampling areas did not reveal a characteristic pattern for each geographic region, nor by culture company. However, some differences were noted between companies with healthy larval cultures and one company which was experiencing mass larval mortalities, emphasizing the relevance of the bacterioplankton in scallop cultures.